Various types of circuits have been proposed to reduce color interference, or undesired mixing of signals within a TV coding network. Some such circuits are located in the luminance channel of a color television (TV) coding apparatus. A circuit which has been proposed--see German patent disclosure document DE-OS 24 11 296--provides for transmission of the luminance signal in two channels--on one channel unchanged and in another channel through a band-pass. The two channels are supplied to the respective inputs of the subtraction circuits. Those spectral portions which are within the range of the auxiliary chroma carrier and occur in the luminance signal are thereby suppressed. The sharpness of the TV image is, however, impaired since these portions contribute to sharpness and definition of the TV image which is to be reproduced. To decrease loss of sharpness, the output signals of the band filter are conducted through a threshold circuit and added to the output signal of the subtraction circuit. This arrangement then provides that, up to a predetermined amplitude, these portions continue to be conductive and may contribute to the sharpness of the viewed image.
It has also been proposed to provide a chroma carrier filter, or blocking circuit, within the luminance channel of the coder. The damping, that is, the band block, can be controlled by a control voltage. The control voltage is derived by measuring the amplitude of the portions of the luminance signal within the range of the chrominance subcarrier.
Both circuits have some disadvantage; the first circuit above described does not optimally suppress the portions of the luminance signals which are within the range of the chrominance subcarrier for all possible images or scenes to be reproduced. The second circuit has the disadvantage that the blocking circuit within the luminance channels causes undesired phase shifts which may lead to the appearance of edge effects, or random oscillations.